1. Field of the Invention
Example embodiments of the present invention relate to a semiconductor memory device and a method of operating the same, and more particularly, to a phase change random access memory (PRAM) and a method of operating the same.
2. Description of the Related Art
A phase change layer of a phase change random access memory (PRAM), in which data is recorded, has a crystal structure or an amorphous structure depending on a heating temperature and a cooling speed. When the phase change layer has a crystal structure, a resistance of the PRAM is low, and when the phase change layer has an amorphous structure, a resistance of the PRAM is high. A PRAM is a nonvolatile memory device capable of recording and reading data using the resistance characteristic.
A problem occurring in a conventional PRAM is that a reset current Ireset necessary to change the phase change layer into an amorphous structure is high.
In order to increase an integration density of a typical PRAM comprising a storage node including a phase change layer in one cell, and one transistor, respective sizes of the storage node and the transistor must be reduced.
However, when the size of the transistor is reduced, because a maximum current allowed in the transistor is reduced, if a reset current is higher than the maximum current of the transistor, data storage using the phase change characteristic may be impossible. Therefore, it is difficult to increase an integration density of a PRAM without a reduction of the reset current of the PRAM.